1. Field of the Invention
This invention relates to an image signal processing apparatus and method. More specifically, the invention relates to the processing and encoding/decoding of an image signal.
2. Description of the Related Art
Recently, as a result of progress in digital signal processing techniques, image apparatuses have been developed in which a large amount of digital information representing moving images, still images and the like is subjected to high-efficiency encoding, and the obtained signal is recorded on a small-size recording medium or transmitted to a communication medium. Digital information recorded on or transmitted to various kinds of media is utilized for various kinds of uses not only by reproducing the information in the form of an image but also by receiving the information in a computer and processing the received information.
Conventional image apparatuses for performing digital signal processing of moving images or still images intend to improve the resolution of the images by using vertically long pixels. For example, in many digital image apparatuses, an image having an aspect ratio of 3:4 is formed by arranging 480 pixels in the vertical direction and 720 pixels in the horizontal direction, each pixel having an aspect ratio of 9:8.
On the other hand, in conventional image processing using a computer, square pixels having an aspect ratio of 1:1 are generally used, and in most cases, an image having an aspect ratio of 3:4 is formed by arranging 480 pixels in the vertical direction and 640 pixels in the horizontal direction.
As described above, the aspect ratio of pixels constituting an image differs between image apparatuses and computers. Hence, when exchanging data between an image apparatus and a computer, it is, in most cases, necessary to perform processing for correcting the aspect ratio of an image.
FIG. 1 is a block diagram illustrating an example of the configuration of a conventional high-efficiency encoding/decoding apparatus for correcting the aspect ratio of an image by compressing/expanding an image signal.
In FIG. 1, an image signal representing an image comprising 480 pixels in the vertical direction and 720 pixels in the horizontal direction, each pixel having an aspect ratio of 9:8, is input to an input terminal 101, subjected to compression encoding by a compression unit 102 and is recorded on a recording medium 103.
A signal reproduced from the recording medium 103 is subjected to expansion encoding by an expansion unit 104, and is then subjected to band limitation by a low-pass filter (LPF) 105. Components representing pixels in the horizontal direction in the signal are thinned by a thinning unit 106. By this thinning processing, an image signal representing an image having an aspect ratio of 1:1 and comprising 480 pixels in the vertical direction and 640 pixels in the horizontal direction is output from an output terminal 107.
In the above-described conventional high-efficiency encoding/decoding apparatus, the picture quality is significantly degraded during compression/expansion. Even though the number of pixels is changed by band restriction and thinning, a high-quality image cannot be supplied to a computer. In order to solve such problems, a method of using different high-efficiency encoding apparatuses depending on the aspect ratio of pixels is considered. This approach, however, has the problem that various kinds of formats are produced on the medium, thereby degrading the efficiency of development.